The present invention relates to a library apparatus in which housing units of recording mediums are disposed on at least one side of one traveling path and a plurality of carrying devices for the recording mediums are disposed on the traveling path, and to a control device and a control method of the library apparatus.
In recent years, with a trend toward the multimedia of information, the data have been increasingly growing in quantity. Therefore, a huge quantity of data must be stored and managed in a computer system. There has been increased demands for middle- and large-sized library apparatuses as those for recording and reproducing the data at a high speed.
The middle- and large-sized library apparatus is roughly constructed in the manner which follows. To be specific, a plurality of box-shaped units are connected on both sides along one travelling path (a rail). A carrying device (referred to as an "accessor") for carrying a magnetic tape defined as a recording medium is installed on the traveling path. The plurality of units include a unit (a housing unit) for housing the magnetic tape, a unit (a recording/reproducing unit) for housing a recording/reproducing device of the magnetic tape, and a unit (a control unit) for housing a controller of the accessor. Then, the controller is connected to a host computer for issuing a variety of commands to the library apparatus.
A rocker constructed of a plurality of cells is formed on a surface, facing to the traveling path, of the housing unit, and the magnetic tape is housed in each cell. Further, a slot is formed in a surface, facing to the traveling path, of the recording/reproducing unit. When the magnetic tape-is inserted into the slot, the magnetic tape is loaded into the recording/reproducing device, and data is recorded on or reproduced from the magnetic tape.
Normally two accessors are provided on the traveling path in terms of a high-speed access being required of the middle- and large-sized library apparatus. Each of the accessor fetches the magnetic tape from an appropriate cell of the housing unit in accordance with a drive command generated by the controller, and performs an operation of carrying the magnetic tape to other cell or the recording/reproducing unit, or an operation of carrying again to an appropriate cell the magnetic tape on and from which the recording/reproducing processes have been done.
The control device housed in the control unit is constructed of control modules of two systems corresponding to the respective accessors. The control module comprises a director, an operation control processor of the accessor, a servo control processor, an accessor driving circuit and an accessor position detecting unit. Herein, the director receives a moving command of the magnetic tape from the host computer and also positional data of the accessor from the position detecting unit, and determines an operation of the accessor on the basis of the above command and data. The operation control processor gives the servo control processor an accessor moving command corresponding to the operation determined by the director. The servo control processor supplies the driving circuit with an accessor moving quantity based on the moving command. The driving circuit supplies an accessor actuator with a driving signal corresponding to the accessor moving quantity. The accessor actuator is thereby driven, and the accessor travels on the traveling path.
Further, the directors of the respective control modules are connected to each other, and the moving command of the magnetic tape and the accessor positional data are exchanged therebetween. Then, the respective directors structure an accessor moving sequence to optimize a moving efficiency of the accessors, and thus move the respective accessors (scheduling).
Particularly the middle- and large-sized library apparatus is required to have a large capacity and high-speed accessing, and therefore precise positional control and a high-speed operation are requested of the accessors. In order to satisfy these requests, the accessors are mounted with precision mechanisms. Consequently, a weight of the accessor amounts to approximately 45 kg under the actual condition. Further, accessor travels at a velocity as high as approximately 3.5 m/s in order to actualize the high-speed accessing, and therefore it might happen that the accessors collide with each other.
If the accessor collide with each other, a comparatively large impact is produced by the collision in terms of considering the weights and the traveling speed thereof. Hence, the precision mechanisms of the accessors are damaged, and an error in accuracy occurs, resulting in such a state that both of the accessors might become unusable. The library apparatus is constructed such that all the cartridges can be, even if the accessor of one system becomes unusable due to the collision etc, continuously carried by the remaining accessor of the other system in order to ensure a high reliability when in operation. If the accessors of the two systems fall into the unusable state because of the collision etc, however, the continuance of the carrying operation thereafter becomes impossible. Moreover, the accessor has the precision mechanism and is therefore expensive. If the accessor is damaged, a considerable economical burden is needed for repairing the damaged accessor.
Furthermore, if the accessors collide with each other, the magnetic tape carried by the accessor might be also damaged due to the impact thereof. This damage to the magnetic tape conduces directly to a loss of data, i.e., the greatest fault in the computer system using the library apparatus.
Thus, the damages caused by the collision between the accessors might become tremendous, and it is therefore required that the collision between the accessors be avoided as much as possible in the middle-and large-sized library apparatus.